Reissner-Nordstrom Kretschmann scalar ($\mathcal{K}=48M^2/r^6-96M{Q}^2/r^7+56Q^4/r^8$)

For the Reissner-Nordstrom metric with $F=1-2M/r+Q^2/r^2$, the Kretschmann scalar isThe first expression follows by squaring the independent Riemann curvature tensor components in an orthonormal frame. This Kretschmann scalar diverges at $r=0$ for any nonzero $M$ or $Q$, but is finite at every positive root of $F$. Regular Eddington-Finkelstein coordinates show that those positive roots are coordinate singularities of the static chart. In the extremal case $Q^2=M^2>0$, its horizon value is $8/M^4$.